Photographic sound track scanning apparatus with light flicker compensation



Feb. 7, 1950 J. A. RomGEfls 2,496,959

PHOTOGRAPHIC SOUND TRACK SCANNING APPARATUS WITH LIGHT FLICKER COMPENSATION v Filed Jan. 8, 1947 PROJECTOR F164" LAMP EXCITZ'I? LAMP FIG. 3.

1 ELECTROMAGNE T JOHN A R on @125 I N VEN TOR PROJEUUR MOTOR ATTORNEYS Patented Feb. 7, 1950 PHOTOGRAPHIC SOUND TRACK SCANNING APPARATUS WVITH LIGHT FLICK-ER. COM

PENSATION John A. Rodgers, Rochester, N. Y., assignor'to Eastman Kodak 'Company'f'Rochester, N. 'Y., a

corporationofNew Jersey Applicationdanuary 8, 19%, Serial No. 720.3%1

12 Claims. 1

The-present invention relates to. a device operating upon alternating current and adapted to project a beamof. light of substantially constant lightflux. It more specifically relates to a'sound motion .picturescanningapparatus and still more particularly to an improved sound motion picture scanningapparatus which is adapted to eliminateor substantially reduce speaker hum caused by the cyclic variations in filament brightness of the exciter lamp which result from the use of alternating current to energize the lamp.

In. sound'motion picture projectors, means are provided to translate the light and dark areas of the-sound track into electrical impulses to operatea loud speaker through an amplifier. Usually, this is-accomplished by focusing a thin band or ribbon of light from an exciter lamp upon the sound track of a filmmoving at a uniform velocity. The opacity of the sound track determines the light flux which passes through the film and impinges upon the phototube which is positioned beyond the film. The electrical impulses of, the phototubeso modulated by the sound track, control the audio amplifier and speaker. In :sucha-systemthe exciteriamp must provide a considerable light output .to overcome the operatingineificiencies of the optics, phototube, etc. and consequently requires asubstantial supply of. electrical energy. This is most readily available from the GO-cycle. alternating cu rentsupply used-to operate the projector, the amplifier, etc. This" energy, however, is unfortunately of a pulsatingnatureand, if used directly withoutrectification and filtration, vcauses cyclic variationsxof; filament brightness of the exciter direct current from-a battery. Since this is seldom convenient, alternating current may be rectified and filtered for the purpose but this necessitates relatively bulky, expensive apparatus to supply the fairly heavy current requirements of the filament. An alternative is to employ a power .2. oscillator operating-lat supersonic frequency; but this, on account ofphysicallimitationsv affecting the *{power pack of the machine, requires the use of low-wattage exciter lamps .in amateur equipment.

An efiective yet simple means for eliminating or substantially reducingspeaker hum, caused'by the cyclic variationsin filament brightness occasioned by the use of alternating current, is described by Miller. R. I-Iutchison, Jr, in his application ior U.,=S. LettersEatent, Serial No. 704,399, filed October 19,; .1946- The. means disclosed therein include a reed whiohprojects partially into ithelightbeam scanningthe sound track and which is vibrated. by an .electromagnet connected in parallel with theexciterlamp in the alternating current circuit. The vibrations of the reed are. so synchronized in respect to amplitude and phase with the cyclic. variations in filament brightness that the reed moves into the light beam intercepting a'greater. amount of light flux, as the. light intensityoi the filament is increased, and is withdrawn from the beam intercepting less flux, as the light. intensity .is decreased. By a careful control of'the amplitude and phase of reed displacement the totalv light fiuximpinging upon the sound track can bemade to remain substantially constant. While means are provided to permit the adjustment of both the. amplitude and phase of the reed vibration, it .has been found that the device disclosedin the above-identified application-11s extremely sensitive to changes. in line voltage. Such-variationsin voltage tend to unbalance the systemcausing; the. return of acertain amount of speaker hum. The present invention, therefore, is directed to. an improvement in the device disclosed by- Hutohison in-his application for'U. 'SpLetters: Patent, Serial No. 104,399,,

wherein the system is less sensitive to variations in line voltage and which has certain other advantages thereover as. will be apparent from the following description- It is, therefore, ano'bjectof the present invention to provide. an improved'device which will project a beamof light of substantially constant light flux despite the cyclic variations in filament brightness of the lamp which arecaused by the use of alternating current to energize the lamp.

It is a further object of the present invention to: provide an ir-npi-ovedv sound. motion picture scanning .apparatusinwhich speaker hum, caused by the cyclic variations infilament-brightness of the exciter. lamp occasioned by theuse of alternating current to energize. the. lamp, is eliminated or substantially reduced.

It is a still further object of this invention to provide an improved sound film scanning device in which a reed is caused to vibrate in such manner as to partially occlude the light fiux emitted by an exciter lamp and directed upon the sound track of the film, the vibrations of the reed being synchronized with the cyclic variations in filament brightness of the exciter lamp so that the light flux impinging upon the sound track remains substantially constant;

It is a still further object of this invention to provide an improved device of the character described in which various adjustments may be readily effected in regard to the amplitude and phase of reed displacement whereby the light flux impinging upon the sound track remains substantially constant despite the cyclic variations in filament brightness of the exciter lamp.

It is a still further object of this invention to provide an improved device of the character described which is relatively insensitive to small variations in line voltage which might otherwise tend to unbalance the system and result in speaker hum.

It is a still further object of this invention to tion and arrangement of parts shown and described without departing'from the spirit of the invention as expressed in the accompanying claims. For the purposes of illustration the present invention is described as embodied in a sound motion picture scanning apparatus. It is apparent, however, that the invention is applicable to other devices which operate on alternating current and in which it is desired to project a beam of light of substantially constant light flux. I, therefore, do not wish to be limited to the exact details shown and described as the preferred form only has been shown by way of illustration.

In the drawing: Fig. l is a front elevational view of a sound film scanning apparatus, partly in section, embodying the present invention;

Fig. 2 is a side elevational view, also partly in section, of the same embodiment;

Fig. 3 is a plan view of the same embodiment; and

Fig. 4 is a wiring diagram illustrating the manner in which the elements of the film scanning apparatus are connected into the projection lamp and motor circuit.

The sound film scanning apparatus illustrated in Figs. 1 to 3, comprises the exciter lamp ID, the optical system H, the sound stabilizing and scanning drum l2, the phototube l3, the vibratory mechanism [4 and the electromagnet 15. The Optical system H is adapted to project a beam of light from the exciter lamp I and to focus a thin band of light upon the sound track of the film 16 which is guided through the beam by the drum [2. The light flux in this thin band modified by its passage through the sound track is caused to impinge upon the phototube l3 resulting in the latter emitting electrical impulses, modulated by the sound track. These impulses in turn control the audio amplifier and speaker (not shown). Compensation for the cyclic variations in filament brightness of the lamp l0 which result from the use of alternating current is eifected by the use of the vibratory mechanism 14 actuated by the electromagnet l5. The former includes a reed ll which is caused to vibrate and to project partially into the light beam traversing the optical system H to intercept varying amounts of light flux. The amplitude and phase of reed displacement is so controlled that the reed mechanically valves the light flux as the filament brightness varies whereby the light flux impinging upon the sound track remains substantially constant.

The exciter lamp 19 is mounted in the lamp socket I8 which is fixed relative to the optical system II. It should be understood that while the various elements, such as the lamp socket, the optical system, the scanning drum, the phototube and the electromagnet, are illustrated in the drawing without any apparent connecting brackets or supports, these elements are in fact connected by conventional means to the sound projector. The socket i8 secures the lamp [0 relative to the optical system H in such fashion that the lamp filament is correctly aligned with the optics. The optical system I l includes two convergent lenses l9 and 20, preferably cylindrical, between which is interposed the reed ll, the vibrations of which cause it to intercept varying amounts of light flux. Fixed apertures 2i and 22 are located adjacent the lenses [9 and 20, respectively. Beyond the lens 20 is positioned a third lens 23, also cylindrical, its geometrical axis being parallel to the filament of the lamp it and at right angles to the axes of the cylindrical lenses l9 and 20. The lens 23 focuses that portion of the light flux, which has traversed the lenses [9 and 20 without being intercepted by the reed I 1, as a narrow band of light upon the sound track of the film. The above elements of the optical system H are mounted in a housing 24 which is preferably molded in two sections from a suitable plastic, such as Bakelite, the housing having molded integrally therewith the lens seats and the fixed apertures 2| and 22. The two sections of the housing may be secured together by any suitable means such as by the screws 25, whereby the lens elements are automatically correctly positioned relative to each other. While the housing may be fixedly connected tothe projector proper, provision may be made for small adjustments of the housing as a whole for more precise alignment and focusing of the optics.

The housing 24 serves not only to mount and correctly position the optical elements therein, but also to keep these elements relatively clean and free of dust. It also serves to mount therein the vibratory mechanism id. The latter comprises the reed [7 which is fastened at one end by a rivet 26 or equivalent means within a channel 2'1. The channel is closed along its length by the cover plate 28, the reed i? being normally held in spaced relation with the base of the channel and the cover plat-e. This boxlike enclosure for the reed in efiect air damps the reed to prevent its response to certain mechanical vibrations. Vibration caused by moving parts on the sound projector will tend to drive the reed at its resonant frequency resulting in an objectionable ringing noise in the speaker during projection of the film. This microphonic condition is substantially reduced by the adequate damping of the reed. The free end of the reed H, which is preferably formed of spring steel, is turned sharply outward'p'rojecting out of the open end of the box-like enclosure as noted in Fig. 1. It is this projecting end which by vibrating occludes varying quantities of the light flux traversing the housing 24. The whole vibratory mechanism 14 is secured to a wall of the housing 24 by the rivet 29- or equivalent means. The other end of this mechanism bears freely upon a biasing screw 30 which is threaded into a wall of the housing 24 and is accessible from without the housing. Manipulation of this screw determines the degree to which the reed projects into the light beam. It is obvious that, while the reed I7 is illustrated in the preferred: embodiment .of the. invention as being positioned between the lenses l9 and 26, it may theoretically be so located as to project into the light beam at any point between the exciter lamp and the film. Practical considerations of available space, housing and protection of the reed, etc. have resulted in the reed being positioned as illustrated in Fig. l.

The resonant frequency selected for the reed is determined in part by the frequency of the variations in filament brightness and, therefore, by the frequency of the alternating current. It has been found that for a 66-cycle power supply a reed having a natural period of vibration of about 100 cycles per secondis preferred. Reeds having natural periods below 80 cycles tend to vibrate at 60 cycles instead of at the 120 cycles desired. Also, reeds having natural frequencies very close to 120 cycles are considerably aiiected asto phase and amplitude of motion by even slight changes in ambient temperature and line voltage. The use of reeds having too high a natural frequency results in considerable micro phonic disturbances arising from vibrations caused by moving parts of the projector.

The electromagnet I5 is located wholly without the housing 26 and is positioned adjaoentfto the wall of the housing upon which the vibratory mechanism i l is mounted. The electromagnet comprises a coil element SI of relatively low re sistance and an iron core 32 which is threaded into the coil element whereby its position T813." tive thereto is adjustable longitudinally. The core 32 is provided with a slotted end for the reception of a screwdriver head by which the core may be advanced or retracted relative to the coil to vary the magnetic air gap between the core and the reed. This adjustment aifects the amplitude of reed vibration. But not..only is it necessary to adjust the amplitude of reed vibration but the phase as well, in order that the amount of light flux intercepted may be so proportional to the filament brightness that the light fiux impinging upon the sound track may remain substantially constant. Moreover, the device should be relatively insensitive to small changes in line voltage which would otherwise tend to unbalance the system causing the return of a certain amount of speaker hum. By cone necting the coil Si in series with the exciter lamp and by employing a long core of relatively small diameter to increase magnetic saturation in the core, it is possible to vary the power supply voltage over a reasonable range of values without any objectionable effect upon the balance. Since the light fluctuations of the lamp filament lag the lamp voltage by some definite amount, it is necessary to produce a phase lag in the vibration of the reed corresponding to this. By using an abnormally long core the required phase lagsna yibe obtained. However, by employing a shading-pole device-the objectionable length of core may be eliminated; This device may take the form of the copper slug or ring 33 threaded upon the "core-between the coil and the reed; the phase lag may thus be varied by adjusting the position of the copper ring 33 upon the core 32. The core is preferably formed of iron or some other material having a low magnetic remanence. A further advantage of a series-connected coil over the parallel-connected coil, such as is disclosed inthe above-mentioned Hutchisonapplication, lies in the fact that should the exciter lamp Iil burn out the circuit is opened, thus preventing damage to the coil 3! or the projectionla-mp 38. This is obviously not the case in the parallel-coil arrangement.

The theory underlying the operation of the sound film scanning apparatus and, in particular, the phase relationships involved is fully discussed in the saidl-Iutchison application for U. S. Letters Patent Serial No. 704,399.

The beam of uni-form light flux is emitted from'the housing 26 through the slot aperture 34 which is aligned with the sound track of the film E6, the latter being guided past the aperture by the sound scanning and stabilizing drum l2. The sound track of the film overlies the edge of the drum l2 as illustrated in Figs. 2 and 3, Whereb'y'the beam may traverse the track, and then be directedupon the phototube it by the reflector unit 35. The latter is preferably a glass or plastic light-conductingrod having an inclined,- mirror'surface 36 at one end which de-. fiects the modulated beam through the rod toward the-phototube. The shaft 3i mounting the drum l2 also preferably mounts a flywheel (not shown) which assists in carrying the film past theaperture 34 at a uniform rate of speed.

It should be understood that the sound film scanning apparatus described herein is equally well adapted for use with films having sound tracks of either the variable density or the variable area. types. It is also. apparent that the beam of'light falling upon the sound track need not be in. the form of a thin or narrow band of light. A beam or, any cross section, covering the width of the sound track, would perform satisfactorily with a mask, or preferably a cylindrical lens and a mask, interposed between the" film and the phototube to cause but a thin transverse band of light of the total beam scanning the sound strip to impinge upon the photo tube. The present invention is obviously adapted to insure that a substantially uniform light flux impinge upon the sound track regardless of the cross section of the beam.

From the foregoing description, it will be ap parent that I have provided means for obtaining all the objects and advantages of this invention. v WhatI claim, and desire to secure by Letters Patent of. the United 'States is: p 1. In a device for use with alternating current adapted. to project a beam of light of substantially constant light flux, a lamp, an optical sys-' tem adapted toproject a beam of light from the lamp, areedcapable of being vibrated and projected partially into the light beam to intercept varying amounts of light flux, an electromagnet adjacent to said reed and connected in series with the lamp, the electromagnet being adapted to vibrate said reed in synchroni'sm with the cyclic variations in lamp brightness, and means to adjust the phase of the reed vibrations relative to' theyarlations in lamp brightness, whereby the light flux of the beam emitted by the device remains substantially constant.

2. In a device for use with alternating current adapted to project a beam of light of substantially constant light flux, a lamp, an optical system adapted to project a beam of light from the lamp, a reed capable of being vibrated and projected partially into the light beam to intercept varying amounts of light flux, an electromagnet positioned adjacent to said reed, the electromagnet including a coil connected in series with said lamp and an adjustable core for varying the air gap between the reed and core, the electromagnet being adapted to vibrate said reed in synchronism with the cyclic variations in lamp brightness whereby the light flux of the beam emitted by the device remains substantially constant.

3. In a device for use with alternating current adapted to project a beam of light of substantially constant light flux, a lamp, an optical system adapted to project a beam of light from the lamp, 2. reed capable of being vibrated and projected partially into the light beam to intercept varying amounts of light flux, an electromagnet adapted to vibrate the reed, the electromagnet including a coil connected in a series with said lamp and a core whose position in the coil is adjustable for varying the air gap between the reed and the core, said core having a shadingpole element adjustably mounted thereon, whereby the reed may be caused to vibrate in such synchronism with the cyclic variations in lamp brightness that the total light flux of the beam emitted by the device remains substantially constant.

4. In a device for use with alternating current adapted to project a beam of light of substantially constant light flux, a lamp, an optical system adapted to project a beam of light from the lamp, a reed capable of being vibrated and projected partially into the light beam to intercept varying amounts of light flux, an electromagnet adapted to vibrate the reed, the electromagnet including a coil connected in series with said lamp and a core threaded into the coil for adjusting the air gap between the reed and the core, said core having a shading-pole element threaded upon the core between the reed and the coil, whereby the reed may be caused to vibrate in. such synchronism with the cyclic variations in lamp brightness that the total light flux of the beam emitted by the device remains substantially constant.

5. In a device for use with alternating current adapted to project a beam of light of substantially constant light flux, a lamp, an optical system adapted to project a beam of light from the lamp, a reed capable of being vibrated and projected partially into the light beam to intercept varying amounts of light flux, an electromagnet adapted to vibrate the reed, the electromagnet including a coil connected in series with said lamp and a core threaded into the coil for adjusting the air gap between the reed and the core. said core being of a relatively smalldiameter to increase magnetic saturation therein and having a phase-controlling element threaded for adjust ment thereon between the reed and the coil, whereby the amplitude and phase of reed vibration may be readily adjusted.

6. In a device for use with alternating current adapted to project a beam of light of substan-. tially constant light flux, a lamp, an optical sys iii Ill

tem adapted to project a beam of light from the lamp, an air-damped reed capable of being vibrated and projected partially into the light beam to intercept varying amounts of light flux, means for adjusting the position of the end of the reed relative to the light beam, an electromagnet adapted to vibrate the reed, the electromagnet including a coil connected in series with said lamp and a core threaded into the coil for adjusting the air gap between the reed and the core, said core being of a relatively small diameter to increase magnetic saturation and having a copper ring threaded thereon between the reed and the coil, whereby the reed may be caused to vibrate in such synchronism with the cyclic variations in lamp brightness that the total light flux of the beam emitted by the device remains substantially constant.

'7. In a sound film seaming apparatus adapted for use with alternating current, an exciter lamp, an optical system adapted to project a beam of light upon the sound track of the film, a phototube optically aligned with said lamp and. optical system and positioned to receive light which has traversed the sound track, a reed capable of being vibrated and projected partially into the light beam to intercept varying amounts of light flux, an electromagnet adjacent to said reed and connected in series with the exciter lamp, the electromagnet being adapted to vibrate said reed in synchronism with the cyclic variations in lamp brightness, and means on said electromagnet to adjust the phase of the reed vibrations relative to the variations in lamp brightness, whereby the light flux impinging upon the sound track remains substantially constant.

8. In a sound film scanning apparatus adapted for use with alternating current, an exciter lamp, an optical system adapted to project a beam of light upon the sound track of the film, a phototube optically aligned with said lamp and optical system and positioned to receive light which has traversed the sound track, a reed capable of being vibrated and projected partially into the light beam to intercept varying amounts of light flux, an electromagnet positioned adjacent to said reed, the electromagnet including a coil connected in series with said exciter lamp and an adjustable core for varying the air gap between the reed and core, the electromagnet being adapted to vibrate said reed in synchronism with the cyclic variations in lamp brightness whereby the light flux impinging upon the sound track remains substantially constant.

9. In a sound film scanning apparatus adapted for use with alternating current, an exciter lamp, an optical system adapted to project a beam of light upon the sound track of the film, a phototube optically aligned with said lamp and optical system and positioned to receive light which has traversed the sound track, a reed capable of being vibrated and projected partially into the light beam to intercept varying amounts of light flux, an electromagnet adapted to vibrate the reed, the electromagnet including a coil connected in series with said exciter lamp and a core whose position in the coil is adjustable for varying the air gap between the reed and the core, said core having a shading-pole device adjustably mounted thereon, whereby the reed may be caused to vibrate in such synchronism with the cyclic variations in lamp brightness that the total light flux impinging upon the sound track remains substantially constant.

10. In a sound film scanning apparatus adapted for use with alternating current, an exciter lamp, an optical system adapted to project a beam of light upon the sound track of the film, a phototube optically aligned with said lamp and optical system and positioned to receive light which has traversed the sound track, a reed capable of being vibrated and projected partially into the light beam to intercept varying amounts of light flux, an electromagnet adapted to vibrate the reed, the electromagnet including a coil connected in series with said exciter lamp and a core threaded into the coil for adjusting the air gap between the reed and the core, said core having a shading-pole device threaded upon the core between the reed and the coil, whereby the reed may be caused to vibrate in such synchronism with the cyclic variations in lamp brightness that the total light flux impinging upon the sound track remains substantially constant.

11. In a sound film adapted for use with alternating current, an exciter lamp, an optical system adapted to project a beam of light upon the sound track of the film, a phototube optically aligned with said lamp and optical system and positioned to receive light which has traversed the sound track, a reed capable of being vibrated and projected partially into the light beam to intercept varying amounts of light flux, an electromagnet adapted to vibrate the reed, the electromagnet including a coil connected in series with said exciter lamp and a core threaded into the coil for adjusting the air gap between the reed and the core, said core being of a relatively small diameter to increase magnetic saturation therein and having a phase-controlling element threaded for adjustment thereon between the reed and the coil, whereby the amplitude and phase of reed vibration may be readily adjusted.

12. In a sound film scanning apparatus scanning apparatus adapted for use with alternating current, an exciter lamp, an optical system adapted to project a beam of light upon the sound track of the film, a phototube optically aligned with said lamp and optical system and positioned to receive light which has traversed the sound track, an airdamped reed capable of being vibrated and projected partially into the light beam to intercept varying amounts of light flux, means for adjusting the position of the end of the reed relative to the light beam, an electromagnet adapted to vibrate the reed, the electromagnet including a coil connected in series with said exciter lamp and a core threaded into the coil for adjusting the air gap between the reed and the core, said core being of a relatively small diameter to increase magnetic saturation therein and having a copper ring threaded thereon between the reed and the coil, whereby the reed may be caused to vibrate in such synchronism with the cyclic variations in lamp brightness that the total light flux impinging upon the sound track remains substantially constant JOHN A. RODGERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,974,900 Shoup Sept. 25, 1934 2,036,447 Tuttle Apr. '7, 1936 2,169,405 Cooney Aug. 15, 1939 2,274,530 Collins Feb. 24, 1942 FOREIGN PATENTS Number Country Date 367,591 Great Britain Feb. 25, 1932 

